Performance requirements for fuel nozzles of gas turbine engines have become increasingly demanding over the past several years. New higher efficiency engines are being operated over a wider range of operating conditions and historical aircraft operating patterns are being markedly changed in the interest of conserving fuel. Fuel flow rates may vary from less than ten (10) pounds per hour to more that eight hundred (800) pounds per hour. At the same time emissions requirements are becoming more stringent. The length of time between engine hot section overhauls is increasing and, in certain applications, there is an increasing interest in the use of lower grade fuels.
Nozzles typical of the prior art applicable to the present invention can be grouped into two general classes, "duplex nozzles" and "pure airblast nozzles". Duplex nozzles comprise a pressure atomizing component for low fuel flow operation and an airblast atomizing component for operation at high fuel flow rates. Two separate and synchronized fuel control systems are required.
Pure airblast nozzles utilize airblast over the full range of engine operation. Such a nozzle typical of those used in advanced commercial gas turbine engines is shown in FIG. 1 (Prior Art). Fuel is injected through a pressure atomizing nozzle "A"; pressurized air is sprayed into the combustion chamber at the core "B" of the nozzle and at the outer periphery of the fuel flow "C" of the nozzle. An American Institute of Aeronautics and Astronautics paper entitled "Influences on Fuel Spray Circumferential Uniformity" by T.J. Rosjford and S. Russell, AIAA-87-2135 dated June 29, 1987, presents a sensitivity analysis and discusses detailed design features of advanced airblast nozzles.
Modern airblast nozzles use a delicate balance of air and fuel flow momenta to achieve high levels of atomization. As a consequence, these nozzles are particularly susceptible to perturbations which can result in undesirable fuel patterns. Such nozzles of the past have generally performed poorly at low fuel flow conditions, and at times have shown poor circumferential uniformity at high fuel flow rates. Scientists and engineers are in search of new advances capable of improved operation at one or both of these conditions.